Process for producing a self-heating auto regulating connector

ABSTRACT

This invention relates to heat-recoverable devices that are self-heating and auto-regulating. The heat-recoverable articles of this invention comprise the combination of a heat-recoverable material and lossy heating particles, such as ferromanetic or ferrimagnetic particles, which produce heat when subjected to an alternating magnetic field and have a Curie temperature at or above the recovery temperature of the material and preferably below the decomposition temperature of the material. The particles can be in an electrically non-conductive layer, on or in thermal contact with the heat-recoverable material or can be dispersed in the heat-recoverable material. The system of this invention includes the heat-recoverable device or article, an induction coil for producing the magnetic field and an alternating current power supply for the induction coil. Preferably the power supply is high frequency and constant current, which produces efficient heating and preferred auto-regulating properties. Preferred particles are small particle size ferrites.

RELATED APPLICATION

This application is a division of U.S. patent application Ser. No.08/014,164 filed Feb. 5, 1993, now U.S. Pat. No. 5,319,173, which is adivision of U.S. patent application Ser. No. 07/404,621, filed Sep. 8,1989, now U.S. Pat. No. 5,208,443 which is a continuation-in-part ofU.S. patent application Ser. No. 07/242,208 filed Sep. 9, 1988, nowabandoned.

FIELD OF THE INVENTION

This invention relates to heat-recoverable articles, sleeves, andconnectors and more particularly relates to the temperatureauto-regulated devices and methods providing proper heating for recoveryof such heat-recoverable articles.

BACKGROUND OF THE INVENTION

The prior art relating to heat-recoverable articles illustrates manydifferent means to effect heating and thereby to recoverheat-recoverable articles. These means include hot air, infraredradiation, ultrasonic vibration, chemical exotherm, open flame, andelectrical resistance heating. All of these methods suffer from variousdisadvantages, one of which is insufficient control which either leadsto overheated and/or excess temperature conditions which damage theheat-recoverable material, or to under-heated and/or insufficienttemperature conditions which result in insufficient recovery of theheat-recoverable article. Other problems occur when the correcttemperature is achieved, but the temperature is not maintained at therequired level for a sufficient period of time to allow complete ordesired recovery of the heat-recoverable article. In one regard, it canbe seen that the prior art devices and methods are veryenergy-inefficient, particularly those in which heat is supplied from anoutside source to the outside surfaces of the heat-recoverable article,thereby causing a significant waste of heat and energy. This also limitsthe applicability of the prior art devices and methods.

Additional problems occur due to non-uniform heating of the mass of therecoverable material in the heat-recoverable article. Thus, inheat-recoverable articles in which the heat-recoverable material is ofan even thickness or even mass distribution, the problem has been toobtain uniform or even heating of the heat-recoverable material toassure uniform recovery. In other articles wherein the thickness or massof the heat-recoverable material differs in various parts of theheat-recoverable article, the problem has been to obtain appropriateheat distribution and sufficient heating in each of the various areas ofdifferent thickness or different mass in order to achieve sufficientrecovery of the higher mass areas without overheating the areas of lowermass.

Various devices and methods have been attempted in order toauto-regulate or enable an operator to control the heating ofheat-recoverable articles. For example, in Glover et al., U.S. Pat. No.4,228,761, and in DeBlauwe, U.S. Pat. No. 4,450,023, thermochromiccoatings are disclosed for visual indicators showing the desiredtemperature of the article has been attained for sufficient recovery andheating of other materials and components present. However, it should benoted that such indicators provide no means of control or regulation ofthe heating, but merely provide a visual indication to an operator whocan, in turn, control the heating, such as by stopping the applicationof heat.

Various other attempts have been made to provide a limited amount ofheat or to provide self-regulating heating means for heat-recoverablearticles. In Deal et al., U.S. Pat. No. 3,551,223, a pyrotechnic coatingis disclosed for supplying a specified amount of heat toheat-recoverable articles. In Diaz, U.S. Pat. No. 4,223,209, and Horsma,et al., U.S. Pat. No. 4,654,511, self-regulating conductive polymerheating devices are disclosed for use with heat-recoverable articles.

These and other devices and methods for providing controllable orself-regulating, properly proportioned heating for heat-recoverablearticles have not produced satisfactory results for a number of reasons.A primary cause of the problems and difficulties in achieving the properor desired control of temperature and the desired proportioning ofheating is due to the fact that as the heat-recoverable articlerecovers, the shape, dimensions, geometry, thickness, and other physicalcharacteristics of the heat-recoverable article change drastically--andin many cases change non-uniformly over the different parts and areas ofthe heat-recoverable article.

In addition, the geometric problems are further complicated by the factthat the geometry is constantly changing while the recovery of thearticle is occurring. Consequently, the thermochromic coating indicatorsare frequently inadequate to indicate whether the desired temperature orheating has been achieved in particular areas of the article. In thickwalled atricles the thermochromic coating only indicates the surfacetemperature and does not indicate the internal temperature of thearticle. Also, erroneous or inadequate indications are given when hotair or open flame is used, because the coating is heated firstSimilarly, the changing geometry and configuration of heat-recoverablearticles as they recover results in various complications and problemsassociated with the use of the above-mentioned self-regulatingconductive polymer heating elements.

A number of the above disadvantages have been overcome by Derbyshire. Asdisclosed by Derbyshire in co-pending U.S. patent application Ser. No.445,819 filed Dec. 1, 1982, now abandoned and corresponding to U.S. Pat.No. 5,053,959 to PCT International Publication WO84/02098 ApplicationNo. PCT/US83/01851), it has been found to be advantageous to use Curietemperature limited heating for various heat-recoverable articles.Derbyshire discloses the use of ferromagnetic materials having thedesired Curie temperature in electrically conductive layers to provideauto-regulated heating to the Curie temperature of the material uponapplication of an alternating current to the conductive layer offerromagnetic material. The power applied to the ferromagnetic layer isin the form of an alternating current source which produces skin effector eddy current heating in the continuous ferromagnetic layer. As theferromagnetic layer reaches the Curie temperature, the permeability ofthe layer drops and the skin depth increases, thereby spreading thecurrent through the wider area of the ferromagnetic layer until theCurie temperature is achieved throughout and the desired heating isachieved. The alternating current is supplied to the ferromagnetic layereither directly from a power source through electrodes in the conductivelayer of ferromagnetic material or is supplied inductively from anadjacent insulated conductive layer directly powered with thealternating current.

While the Derbyshire type of Curie temperature limited heating ofheat-recoverable materials and articles provides certain advantages andimprovements over other prior art, the Derbyshire skin effect or eddycurrent heating has one aspect which is a disadvantage in manyapplications. The disadvantage is due to the necessity of their beingelectrically conductive layers in the heat-recoverable articles. In manyapplications, it is desirable to have no electrically conductive layersor areas in the heat-recoverable article.

The disclosures of the above references are incorporated herein byreference.

In view of the insufficiencies and certain disadvantages of the aboveprior art devices and articles, it is apparent that there is a need forimproved auto-regulating, heat-recoverable articles. The presentinvention has been developed to provide auto-regulating,heat-recoverable articles as well as systems for using those articleswhich do not suffer from the insufficiencies or disadvantages mentionedabove.

Therefore, it is an object of this invention to provide heat-recoverablearticles which do not require hot air, infrared radiation, ultrasonicvibration, flame, or D.C. resistance heating to effect recovery.

It is a further object of this invention to provide heat-recoverablearticles which are auto-regulating and thereby are protected fromoverheating.

It is a further object of this invention to provide heat-recoverablearticles which can be electrically non-conductive in their entirety orin any desired portion thereof.

It is another object of this invention to provide heat-recoverablearticles which are capable of minimizing the energy requirementsnecessary for recovery.

It is another object of this invention to provide improved Curietemperature limited heating for heat-recoverable articles by eliminatingthe need for direct electrical connection to the heat-recoverablearticle.

It is another object of this invention to permit easy selection ofprecise Curie temperature limited heatable articles and to tailor theCurie temperature to particular needs without concern for incorporatingelectrically conductive layers or electrical connections in the article.

It is another object of this invention to provide an improvedself-heating soldering device incorporating a self-heating,heat-recoverable sleeve with a solder preform located inside the sleeve.

It is another object of this invention to provide an improvedheat-recoverable article incorporating a fusing material, such assolder, or a thermoplastic material within a tubular member which isauto-regulating at a Curie transition temperature which is above theactivation temperature of the fusing material, above the recoverytemperature of the heat-recoverable material, and is below thedegradation temperature of those materials.

These and other objects are achieved by the present invention as will berecognized by one skilled in the art from the following summary anddescription of this invention.

SUMMARY OF THE INVENTION

In one aspect, this invention is a self-heating, heat-recoverablearticle for use in an alternating magnetic field, comprising:

a) a layer of heat-recoverable material having a recovery temperature T,and

b) an electrically non-conductive layer of lossy heating particleshaving a Curie temperature of T or greater whereby said particles arecapable of producing heat when subjected to an alternating magneticfield,

said layer of particles being in thermal contact with said layer andthereby being capable of heating said material to at least a temperatureof T upon the article being subjected to said alternating magneticfield.

In another aspect, this invention is a self-heating, heat-recoverablearticle for use in an alternating magnetic field, comprising:

a layer of heat-recoverable material having a recovery temperature T andhaving dispersed in said material lossy heating particles having a Curietemperature of T or greater, whereby said particles are capable ofheating said material to at least a temperature of T upon beingsubjected to an alternating magnetic field, and wherein said particlesare arranged in said material such that the particles do not provide anelectrically conductive path in said material.

In another aspect, this invention is a method of providing aself-heating, heat-recoverable article for use in an alternatingmagnetic field comprising:

applying an electrically non-conductive layer of lossy heating particleshaving a Curie temperature of T or greater to a surface of aheat-recoverable article having a recovery temperature T.

In another aspect, this invention is a method of providing aself-heating, heat-recoverable article comprising:

incorporating into a heat-recoverable material having a recoverytemperature T an effective amount of lossy heating particles which havea Curie temperature of T or greater such that said particles do notprovide an electrically conductive path in said material; and

forming a heat-recoverable article.

In another aspect, this invention is a method of protecting a substratecomprising:

placing over the substrate a self-heating, heat-recoverable articlecomprising:

a) a layer of heat-recoverable material having a recovery temperature T,and

b) an electrically non-conductive layer of lossy heating particleshaving a Curie temperature of T or greater whereby said particles arecapable of producing heat when subjected to an alternating magneticfield,

said layer of particles being in thermal contact with said layer andthereby being capable of heating said material to at least a temperatureof T upon the article being subjected to said alternating magneticfield; and

subjecting said article to an alternating magnetic field to effectrecovery of the article onto the substrate.

In another aspect, this invention is a self-heating sleeve, comprising:

a) a layer of material deformed into a heat dimensionally unstableconfiguration, said material possessing a transition temperature T atwhich temperature it substantially recovers to its undeformed heatdimensionally stable configuration, and

b) electrically non-conductive highly lossy ferromagnetic particlespossessing a Curie temperature greater than T achievable upon exposureto an alternating magnetic field,

said particles being in intimate contact with said layer.

In another aspect, this invention is a process for producing aself-heating, auto-regulating connector, comprising the steps of:

a) deforming a first dimensionally heat-stable sleeve to render thesleeve dimensionally heat-unstable at temperature T,

b) coating the first sleeve with an electrically non-conductive layer ofhighly lossy, ferromagnetic particles having a Curie transitiontemperature greater than T,

c) deforming a second dimensionally heat-stable sleeve to adimensionally heat-unstable configuration at temperature T,

d) positioning the second sleeve over the first sleeve so the coatedparticles are in contact with the second sleeve to form a compositesleeve, and

e) exposing the combined sleeve to an alternating magnetic field causingthe particles to heat to their Curie transition temperature which causessaid first and second sleeves to substantially return to theirdimensionally heat-stable configuration.

In another aspect, this invention is an auto-regulating system forrecovering heat-recoverable articles comprising, in combination:

a self-heating, heat-recoverable article for use in an alternatingmagnetic field, comprising:

a) a layer of heat-recoverable material having a recovery temperature T,and

b) an electrically non-conductive layer of lossy heating particleshaving a Curie temperature of T or greater whereby said particles arecapable of producing heat when subjected to an alternating magneticfield,

said layer of particles being in thermal contact with said layer andthereby being capable of heating said material to at least a temperatureof T upon the article being subjected to said alternating magneticfield;

an induction coil adapted to produce said magnetic field; and

a power supply being adapted to provide power to the induction coil asalternating current at a preselected frequency effective for heatingsaid particles.

In another aspect, this invention is an assembly comprising:

an induction coil adapted to produce a magnetic field;

a self-heating, heat-recoverable article positioned in said magneticfield and comprising:

a) a layer of heat-recoverable material having a recovery temperature T,and

b) an electrically non-conductive layer of lossy heating particleshaving a Curie temperature of T or greater whereby said particles arecapable of producing heat when subjected to an alternating magneticfield,

said layer of particles being in thermal contact with said layer andthereby being capable of heating said material to at least a temperatureof T upon the article being subjected to said alternating magneticfield; and

a power supply connected to said induction coil, said power supply beingadapted to provide power to the induction coil as alternating current ata preselected frequency effective for heating said particles.

In preferred aspects, this invention provides the above articles,methods, systems and assemblies wherein the articles include connectorswhich contain fusible materials such as solder. In other preferredaspects, the power supply used in this invention is preferred to be aconstant current power supply, which provides certain advantages withrespect to the auto-regulation aspects of this invention.

BRIEF DESCRIPTION OF THE DRAWING

FIG. 1 is a cutaway side view of a heat-recoverable connector inaccordance with this invention.

FIG. 2 is a cross-sectional view of a sheet made in conformity with thisinvention.

FIG. 3 illustrates particles dispersed throughout a sleeve made byco-extrusion.

FIG. 4 illustrates particles dispersed throughout a sleeve which has asolder preform.

FIG. 5 illustrates particles dispersed throughout a sleeve which hasmeltable thermoplastic inserts and a solder preform.

FIG. 6 illustrates a cross-sectional view of a double sleevearrangement.

FIGS. 7 and 8 illustrate systems and assemblies according to thisinvention.

DETAILED DESCRIPTION OF THE INVENTION

This invention is based at least in part on the realization anddiscovery that sufficient heat can be applied to heat-recoverablearticles in an auto-regulated manner to efficiently recover theheat-recoverable article in a manner such that overheating andunder-heating areas of the articles are avoided. This invention is alsoat least in part based upon the realization that the entire power andenergy for recovering the heat-recoverable device can be provided by anexternal alternating magnetic field--without the need for applyingexternal heat, without the need for supplying any electrical current toor through the heat-recoverable article itself, and without the need forthe heat-recoverable article to contain any electrically conductivelayers, areas, or contacts.

This invention comprises a particular combination of heat-recoverablematerial with "lossy heating particles" having a specific thermal andfunctional relationship with the heat-recoverable material. The lossyheating particles may be present in a layer on the surface of theheat-recoverable article or on the surface of the heat-recoverablematerial in the article, or may be dispersed in the heat-recoverablematerial or otherwise positioned in the atricle, as long as the heatfrom the lossy heating particles can effectively reach theheat-recoverable material. The "layer" of lossy heating particles may bepresent as particles dispersed in the heat-recoverable material ordispersed in another material layer adjacent to or in thermal contactwith the heat-recoverable material. This particle layer is electricallynon-conductive, due either to the arrangement of the particles or to theproperties of the particles themselves. In this respect it is generallypreferred to use electrically non-conductive ferrimagnetic particlesand, more preferably, ferrite particles. Alternatively, if electricallyconductive particles are used, they may be dispersed in or on theheat-recoverable material in such a fashion that the particles do notform electrically conductive pathways through or on the heat-recoverablematerial. Also, if it is desired to use electrically conductiveparticles, they can be coated with an electrically insulating layer orcan be dispersed in a binder material which electrically insulates thearticles from each other to prevent them from forming an electricallyconductive pathway or layer.

The term "lossy heating particles" as used herein means any particlehaving particular properties which result in the particles being capableof generating sufficient heat for purposes of this invention whensubjected to an alternating magnetic field having a specified frequency.Thus, any particle having these properties and being useful in thepresent invention is within the scope of this definition. As pointed outherein, there has been inconsistent and/or confusing terminology used inassociation with particles which respond to magnetic fields. While notbeing bound by particular terminology, the lossy heating particlesuseful in this invention generally fall into the two categories ofparticles known as ferromagnetic particles and ferrimagnetic particles.

In general, the ferrimagnetic particles, such as ferrites, are preferredbecause they are usually non-conductive particles and because theyproduce heat by hysteresis losses when subjected to an alternatingmagnetic field. Therefore, ferrimagnetic particles will produce heatingby hysteresis losses in the appropriate alternating magnetic field,essentially regardless of whether the particle size is large or small.

Also useful in this invention, and preferred in some applications, arethe ferromagnetic particles which are electrically conductive.Ferromagnetic particles will produce heating dominated by hysteresislosses if the particle size is small enough. However, sinceferromagnetic particles are conductive, large particles will producesignificant eddy current losses at the skin or surface thereof.

It is generally preferred in the practice of this invention to provideheating by hysteresis losses because, the particle size can be muchsmaller for effective hysteresis loss heating than with effective eddycurrent surface heating, i.e., for hysteresis loss heating, the smallerparticle size enables more uniform heating of the article and does notdegrade the mechanical properties of the material, because the smallerparticles can be more dispersed than larger particles. The moredispersed, smaller particles thereby usually provide more efficientheating. However, the particle size is to be at least one magneticdomain in diameter in order to provide the necessary coupling with thealternating magnetic field, i.e., the particles are prefferably as smallas practical but are multi-domain particles.

The heating produced by the lossy heating particles useful in thepresent invention can be either provided by or can be enhanced bycoating the particles with an electrically-resistive coating. As will berecognized by one skilled in the art, particles that are not lossybecause they do not exhibit hysteresis losses, can be converted to lossyheating particles for use in this invention by placing such a coating onthe particles. The coating produces eddy current losses associated withthe surface effect of the coated particles. At the same time, particleswhich are lossy due to hysteresis losses can be enhanced in theireffectiveness for some applications by such coatings, thereby providinglossy particles which produce heating both by hysteresis losses and byeddy current losses.

Magnetic particles which are useful in the present invention are knownin the art. For example, in White, U.S. Pat. No. 3,319,846, finelydivided (0.01-5 micron), ferrite particles are suspended in or arecoated on a selected heat-activatable material. The material may be inthe form of a thermoplastic, hot-melt adhesives, etc. According toWhite, ferrite particles are exposed to a magnetic field of at least 10megahertz, preferably 40 megahertz, in order to generate the inductiveheating. The particles heat to a maximum temperature referred to as the"Neel" temperature. The Neel transition temperature of the particle(similar to the Curie temperature) is the point at which the magneticfield ceases to have an effect on the particles, and the temperaturereaches a stable maximum. While White's disclosure describes a number ofparticles useful in the present invention, there are other particlesuseful in this invention.

Additionally, it is known that ferrites can possess any range of Curietemperatures by compounding them with zinc, manganese, cobalt, nickel,lithium, iron, or copper, as disclosed in two publications: "TheCharacteristics of Ferrite Cores with Low Curie Temperature and TheirApplication" by Murkami, IEEE Transactions on Magnetics, June 1965, page96, etc., and Ferrites by Smit and Wijn, john Wiley & Son, 1959, page156, etc.

There has been some inconsistent usage of terminology with respect toferromagnetic particles in the past. For example, compare thenomenclature used in White referred to above and in Lee, Magnetism, anIntroductory Survey, Dover Publications, Inc., New York, 1970, FIG. 44,at page 203. The preferred nomenclature is believed to be that of Leeand is primarily used herein. See also Brailsford, Magnetic Materials,Methuen & Co. Ltd., London, 1960.

The term "ferromagnetic" is frequently used to refer to magneticparticles generically regardless of their particular properties. Thus,ferrites have usually been referred to as being "ferromagnetic" orincluded in the general group of ferromagnetic materials. However, forpurposes of this invention, it is preferred to use the terminology shownin FIG. 44 of Lee, referred to above, wherein the magnetic particles areclassified in two groups, ferromagnetic and ferrimagnetic. Theferromagnetic particles are usually considered to be electricallyconductive materials which have various magnetic properties. Theferrimagnetic particles are usually considered to be electricallynon-conductive materials which also have various magnetic properties.Ferrites are usually considered to be electrically non-conductivematerials and are thus in the class of ferrimagnetic materials. Bothferromagnetic materials and ferrimagnetic materials can be low-loss, ornon-lossy, type of materials, which means they do not have significantenergy loss or heat produced when subjected to an electric potential ormagnetic field. These non-lossy type of magnetic materials are the kindused in various electric equipment components, such as ferrite cores forcoils, where no or minimum energy loss/heat production is desired.However, both these materials can also be the high-loss, or lossy, typeof materials, which means they will have significant energy loss andheat production when subjected to an electric potential or magneticfield. It is this class of lossy or highly lossy ferromagnetic andferrimagnetic materials which are useful in the present invention.

Regardless of the labels or terminology for magnetic particles, themagnetic particles useful as and included within the scope of the term"lossy heating particles" for the present invention need merely to havethe following properties: (1) having the desired Curie temperature forauto-regulation of the temperature when subjected to an appropriatealternating magnetic field, and (2) being sufficiently lossy, either byhysteresis losses, by eddy current losses, or both, in order to producethe desired heat when subjected to the alternating magnetic field. Theseparticles are sometimes referred to as being "highly lossy." While thesize of the particles is not particularly important in the presentinvention, it is desirable to use smaller particles since they can bedispersed more uniformly in the heat-recoverable material or article,thus heating more efficiently and uniformly. As recognized by oneskilled in the art, the size of the particle should be no smaller thanone magnetic domain, i.e., the particles should be multi-domain sizeparticles.

As will also be recognized by one skilled in the art, the lossy heatingparticles, the magnetic induction coil, and the frequency, power andcontrol mechanism for the power supply will all be selected for use inthis invention so that they are matched for electrical properties andperformance in the articles and systems as disclosed herein. Forexample, the particle size, the distribution of the particles in theheat-recoverable article, and the permeability of the particles must beconsidered in addition to providing an impedance-matched induction coiland power supply. As indicated herein, a preferred power supply foroptimum self-regulation characteristics is one that is a constantcurrent power supply, but other types of power supplies can be used indifferent embodiments of this invention depending on the particular usesand results desired for the systems of this invention. The factorsinvolved in load matching and power supply/coil characteristics aresimilar to and much the same as in the systems in which ferromagneticparticles are heated by direct application of electric current. Forexample see, U.S. Pat. No. 4,256,945 of Carter et al., U.S. Pat. No.4,695,713 of Krumme, and related patents.

The advent of this invention resulted from efforts to discover aninexpensive, self-heating, auto-regulating heat-recoverable sleeve foruse as a connector and a method for its manufacture and use without theneed for direct connection to a power source. It was found thatheat-shrinkable tubing slipped over an inner sleeve incorporatingparticles which, when subjected to an alternating magnetic field, heatto the Curie temperature of the particles by induction heating generatesufficient heat to cause both sleeves to resume to its original,unexpanded configuration. More precisely, when the outer sleeve (driversleeve) recovers, it forces the inner sleeve (heat-shrinkable or not) tocompress against the member it surrounds. This embodiment of the presentinvention is but one illustration of the wide range of embodimentswithin the scope of the present invention.

For the purpose of experimentation, heat-generating particles weredeposited on the outer surface of the inner sleeve which was thencovered with an additional sleeve. Formation of the particle-containing,heat-recoverable sleeve can also be achieved by co-extrusion of theparticles onto or within the sleeve.

In order to further describe and illustrate the present invention,reference is now made to the drawing attached hereto.

FIG. 1 depicts connector 10 made in accordance with this invention.Connector 10 includes outer tube 12 which is heat-shrinkable, magneticparticle coating 14, and inner tube 16 which is also heat-shrinkable.Disposed within inner tube 16 is solder preform 18. Outer tube 12,referred to herein as driver tube 12, is composed of any conventionalheat-shrinkable material.

Generally, such heat-shrinkable materials are composed of cross-linkedpolymers which have been rendered dimensionally heat-unstable duringprocessing where, upon exposure to heat at or in excess of thecrystalline transition temperature, the material recovers to itsdimensionally heat-stable configuration. As is readily appreciated bythose of ordinary skill in the art, there are many such materials,polymeric or not, exhibiting a large range of crystalline transitiontemperatures which are selected to suit a particular purpose based uponthe physical characteristics of both the material and its crystallinetemperature.

Magnetic particle coating 14 is composed of any appropriate bindingmaterial such as a wax, silicone cement, or simply a layer offinely-ground powder deposited on driver tube 12 by conventionalmechanical or vapor deposition means. The powder, for example, can beFair-Rite (trademark) No. 73 (which is available from Fair-Rite ProductsCorp., Wallkill, N.Y.) which when ground into a fine powder, exhibitsthe characteristics desirable for practice of this invention. Fair-RiteNo. 73, itself, possesses properties including μ_(i) of 2500, μ max of4000, B_(s) gauss at 13 oer of 4000, a Curie temperature of 160° C.,volume resistivity in ohm-centimeter of 100, and H_(c) in oer of 0.18.Both of these materials exhibit a sufficiently lossy nature at 13.56megahertz and far below that frequency to provide the necessaryinduction heating effects at relatively low frequencies.

It has also been found that metal plating the ferrite particles with ahighly electrically-resistive metal enhances heat generation due to eddycurrents established in the resistive plating. It is also possible tocoat the particles with a conductive material, but if a less resistivematerial (metal, conductive polymer, etc.) is employed, then cautionmust be exercised to avoid formation of an electrically conductivepathway between the particles.

Moving now to the composition and structure of inner tube 16, it may beselected from any material as long as it adequately serves topositionally stabilize magnetic particle coating 14 relative to drivertube 12. Hence, inner tube 16 need not necessarily be formed from aheat-recoverable material, but, if not, it must be easily deformable soas not to impede the heat-recovery of driver tube 12 as it shrinksinwardly. However, as a practical matter, inner tube 16 is preferablycomposed of the same material as driver tube 12 and has an outerdiameter corresponding to the inner diameter of driver tube 12.

Where desirable, connector 10 can incorporate solder preform 18 to moresecurely join wires, wire terminals, or the like contained within thetube. The composition of solder preform 18 is of any conventional alloyas long as it is compatible with the foregoing and thus has a meltingtemperature below that of the Curie temperature of the particlescontained in magnetic particle coating 14.

Preferably, solder preform 18 would have a melting temperature tailoredto be less than the Curie temperature of the particles and preferrablyin the same range as the crystalline transition temperature of drivertube 12 whereupon application of the alternating magnetic field willinductively heat the ferromagnetic particles and cause solder preform 18to soften and melt as tubes 16 and 12 contract. The melted solder isthen pressed around wires or other substrates present inside theconnector, then the solder hardens once the application of thealternating magnetic field is terminated, thereby forming a strong,secure connection.

FIG. 2 illustrates tube 20 in sheet form. Like driver tube 12 in FIG. 1,sheet 22 is composed of a heat-shrinkable material. Embedded layer 24,the equivalent of magnetic particle coating 14, comprises thenon-conductive magnetic particles either alone or combined with abonding agent. The sheet form, in contrast to the tube form, isadvantageous in certain applications which do not permit the use of atube. The sheet can be wrapped around a subject member (spliced wires,etc.) and exposed to an appropriate magnetic field to induce heating andheat shrinking.

Referring to the equipment employed in the experimental phase, aconstant current power supply RFG30 available from Metcal, Inc., MenloPark, Calif., having an adjustable current power output control wasselected. This power supply was modified to have a mannual adjustment ofthe level of the current output, but once set it operated at theselected constant current power setting. The power supply was attachedto an inductance coil through a Transmatch III matching networkavailable from MFJ Enterprises, Starkville, Miss. The principalcharacteristics of the coil included 13.5 turns of 0.035 inch (0.89millimeter) diameter HML wire, a length of 0.55 inch (13.97millimeters), and an inner diameter of 0.215 inch (5.46 millimeters).The matching network was tuned to provide an initial maximumtransmission of 5 watts to the induction coil prior to introduction ofconnector 10. Once inserted, connector 10 caused the power to rise toapproximately 13 watts and to auto-regulate down to 8 watts. Thus, a netchange from 8 to 3 watts was exhibited.

Given the foregoing arrangement, a variety of materials was tested.Those materials, particles, power requirements, and recovery time (thetime required to induce substantially complete recovery of thedimensionally heat-unstable materials to a dimensionally heat-stableconfiguration), are provided in Table I.

                  TABLE I                                                         ______________________________________                                        Heat-shrinkable tube composition                                                                     Kynar                                                  (inner and outer)                                                             Tube outer diameter    0.210 inch                                                                    (5.33 mm)                                              Tube wall thickness    0.007 inch                                                                    (0.18 mm)                                              Tube length            0.511 inch                                                                    (12.99 mm)                                             Heating particles      Fair-Rite 73                                                                  powder                                                 Initial power (net)    8 watts                                                Regulated power (net)  3 watts                                                Recovery time          10-15 sec.                                             ______________________________________                                    

FIGS. 3-5 illustrate various arrangements of materials in a plastic tubesuch as the inner tube 16 of FIG. 1. In FIG. 3, plastic tube 31 is of anappropriate thermoplastic with particles 32 dispersed evenly throughout.Without solder or other inserts, the tube can be used merely as a heatrecoverable sleeve. FIG. 4 illustrates the same tube as FIG. 3 withsolder preform 18 disposed within plastic tube 31. In FIG. 1, theparticles are dispersed on surface 14 of the plastic tube 16 and notwithin the plastic. FIG. 5 illustrates meltable plastic inserts 51within the plastic tube 31 of FIG. 3 together with solder preform 18whereby during a single heating operation, solder preform 18 is meltedto join the members, and meltable plastic inserts 51 flow and provide awaterproof seal. Such inserts can be thermoplastic, fusible,thermosetting, self sealing, or other useful inserts.

Referring to FIG. 6, an inner tube 25 has ferrite particles eitherincorporated therein or coated on its outer surface and an outer tube 27of heat-shrinkable material. The inner tube 25 may also, but notnecessarily, be of heat-shrinkable material. Upon heating, the outertube 27 shrinks and collapses the structure about a substrate or memberto be encased.

Referring to FIG. 7, heat-recoverable connector 10 of FIG. 1 is adaptedfor recovering onto and connecting wires 79. Induction coil 73 (shown insection view) is connected to alternating current power supply 74 byleads 75. Preferably, the power supply is a constant current powersupply, as defined and illustrated in U.S. Pat. No. 4,789,767 toDoljack, and U.S. application Ser. No. 169,027, filed Mar. 3, 1988, nowabandoned, both of which are incorporated herein by reference. Theinduction coil, which is adapted for receiving connector 10, generatesan alternating magnetic field in the area of connector 10 causingparticles in layer 14 to heat connector 10, thereby recovering connector10 onto substrates 79.

FIG. 8 illustrates another embodiment for generating the alternatingmagnetic field for use in this invention. Split torrid core 81 generatesa magnetic field in the area adapted for receiving connector 10. Coil 82is connected to alternating current power supply 83 to produce thedesired alternating magnetic field.

As will be recognized by those skilled in the art from the above generaldescription of this invention and the above description of preferredembodiments, the present invention provides a number of advantages overthe prior art devices and methods for heating and recoveringheat-recoverable articles. For example, the present invention is veryefficient in heat and energy usage because the heat and energy issupplied directly to the heat-recoverable material and can be arrangedso the heat is supplied internally in the heat-recoverable article, thuseliminating any exterior waste of heat and energy. Moreover, the presentinvention enables one to use embodiments that are suitable for recoveryof heat-recoverable articles in environments not suitable for recoveryof articles by external heat sources such as a flame. Among thoseenvironments are underground installations such as for telephone cablesand power cables where the use of an open flame or heat sources whichcan possibly ignite combustible gasses are not permitted. Anotherenvironment in which the present invention enables the construction ofembodiments for recovery of heat-recoverable articles is underwaterapplications. Other embodiments for various environments will beapparent to one skilled in the art following the teachings of thisinvention.

It will also be apparent to one skilled in the art that various priorart elements may be used in combination with the present invention. Forexample, thermochromic indicators and coatings may be used on theheat-recoverable articles of the present invention to serve as anindicator and quality control device to assure that the operator retainsthe heat-recoverable article in the alternating magnetic field for asufficient period of time to produce the desired temperature andheating. For example, on a continuous production line, the thermochromicindicator can be used to indicate that the heat-recoverable article hasmoved through the magnetic field at the desired rate and that thedesired Curie temperature was, in fact, reached and/or that the desireddegree of heating has, in fact, occurred.

Indication of sufficient heating is also inherent in the system of thisinvention by monitoring the power supplied to the heat-recoverablearticle by the system. When the article is below the Curie temperature,the system will deliver maximum power to the article. Once the articleis substantially at the Curie temperature, its coupled resistance willdecrease and the power delivered to it will also decrease to a minimumlevel. By monitoring the powere level one can easily determine when thedesired temperature has been reached and can then control the length oftime that the system maintains the article at that temperature by itsauto-regulation capabilities.

Given the foregoing objects, description, and examples of the invention,many variations and modifications, both of the devices and methods,should now be readily apparent to the person of ordinary skill in theart. These variations and modifications are intended to fall within thescope and intent of this invention as defined by the following claims.

I claim:
 1. A process for producing a self-heating, auto-regulating connector, comprising the steps of:a) deforming a first dimensionally heat-stable sleeve to render the sleeve dimensionally heat-unstable at temperature T, b) coating the first sleeve with an electrically non-conductive layer of highly lossy, ferromagnetic particles having a Curie transition temperature greater than T, c) deforming a second dimensionally heat-stable sleeve to a dimensionally heat-unstable configuration at temperature T, d) positioning the second sleeve over the first sleeve so the coated particles are in contact with the second sleeve to form a composite sleeve, and e) exposing the combined sleeve to an alternating magnetic field causing the particles to heat to their Curie transition temperature which causes said first and second sleeves to substantially return to their dimensionally heat-stable configuration.
 2. A process according to claim 1 further including the step of plating the particles with a highly resistive metal to allow eddy currents to be induced in the plated layer.
 3. A process according to claim 1 further including the steps of forming the sleeves wherein the second sleeve surrounds the first sleeve as a tube and inserting a solder preform having a melting temperature below the Curie temperature within the first sleeve. 